Question

The documentation says:

您应该仔细考虑是否要在每次更改时更新表视图。如果同时进行大量修改 - 例如，如果您正在从后台线程读取数据 - /.../，您可以实现controllerDidChangeContent :(在处理完所有挂起的更改时发送给委托）到重新加载表视图。

这正是我正在做的事情：我正在使用不同的ManagedObjectContext处理后台线程中的传入更改，并使用mergeChangesFromContextDidSaveNotification将结果合并到主线程MOC中。到目前为止一切都很好。

我选择不实现controller：didChangeObject：...而是希望执行文档建议的批量更新。

问题/问题：该文档没有详细说明如何实际实施批量更新？我应该在controllerDidChangeContent中调用[tableview reloadData]：还是有一种不那么干扰的方式可以让我免于完全重载？

我有一个想法：我可以注意到mergeChangesFrom ...包含已更改对象的通知，找出它们的索引路径，然后只调用tableview：ReloadRowsAtIndexPaths：for。但是有任何权威信息，建议或例子吗？或者只是[tableview reloadData]？

（旁白：控制器：didChangeObject：...当它收到一组批量更新时开始表现得非常不稳定，即使相同的更新代码[我现在放在后台线程中]在它运行之前运行良好主线程，但当然锁定UI。）

Answer 1

我只需在reloadData中致电controllerDidChangeContent:。

为了动画表的个别更改，Apple的样板代码（iOS SDK 4.3.x）如下所示：

- (void)controllerWillChangeContent:(NSFetchedResultsController *)controller
{
    [self.tableView beginUpdates];
}

- (void)controller:(NSFetchedResultsController *)controller didChangeSection:(id <NSFetchedResultsSectionInfo>)sectionInfo
           atIndex:(NSUInteger)sectionIndex forChangeType:(NSFetchedResultsChangeType)type
{
    switch(type)
    {
        case NSFetchedResultsChangeInsert:
            [self.tableView insertSections:[NSIndexSet indexSetWithIndex:sectionIndex] withRowAnimation:UITableViewRowAnimationFade];
            break;

        case NSFetchedResultsChangeDelete:
            [self.tableView deleteSections:[NSIndexSet indexSetWithIndex:sectionIndex] withRowAnimation:UITableViewRowAnimationFade];
            break;
    }
}

- (void)controller:(NSFetchedResultsController *)controller didChangeObject:(id)anObject
       atIndexPath:(NSIndexPath *)indexPath forChangeType:(NSFetchedResultsChangeType)type
      newIndexPath:(NSIndexPath *)newIndexPath
{
    UITableView *tableView = self.tableView;

    switch(type)
    {

        case NSFetchedResultsChangeInsert:
            [tableView insertRowsAtIndexPaths:[NSArray arrayWithObject:newIndexPath] withRowAnimation:UITableViewRowAnimationFade];
            break;

        case NSFetchedResultsChangeDelete:
            [tableView deleteRowsAtIndexPaths:[NSArray arrayWithObject:indexPath] withRowAnimation:UITableViewRowAnimationFade];
            break;

        case NSFetchedResultsChangeUpdate:
            [self configureCell:[tableView cellForRowAtIndexPath:indexPath] atIndexPath:indexPath];
            break;

        case NSFetchedResultsChangeMove:
            [tableView deleteRowsAtIndexPaths:[NSArray arrayWithObject:indexPath] withRowAnimation:UITableViewRowAnimationFade];
            [tableView insertRowsAtIndexPaths:[NSArray arrayWithObject:newIndexPath]withRowAnimation:UITableViewRowAnimationFade];
            break;
    }
}

- (void)controllerDidChangeContent:(NSFetchedResultsController *)controller
{
    [self.tableView endUpdates];
}

Answer 2

我相信这就是你要找的东西：

而不是打电话

deleteSections
insertSections
reloadSections
deleteRowsAtIndexPaths
insertRowsAtIndexPaths
reloadRowsAtIndexPaths

当更改进入controller:didChangeObject:atIndexPath:forChangeType:newIndexPath时，收集属性中的indexPaths和section。然后在controllerDidChangeContent:。

中执行批处理

参考：http://www.fruitstandsoftware.com/blog/2013/02/19/uitableview-and-nsfetchedresultscontroller-updates-done-right/

修改

以下是链接中提到的方法略有不同，更加人为但又更紧凑的版本：

@property (nonatomic, strong) NSMutableArray *sectionChanges; @property (nonatomic, strong) NSMutableArray *objectChanges; - (void)controllerWillChangeContent:(NSFetchedResultsController *)controller { } - (void)controller:(NSFetchedResultsController *)controller didChangeSection:(id <NSFetchedResultsSectionInfo>)sectionInfo atIndex:(NSUInteger)sectionIndex forChangeType:(NSFetchedResultsChangeType)type { NSMutableDictionary *sectionChange = [NSMutableDictionary new]; switch(type) { case NSFetchedResultsChangeInsert: case NSFetchedResultsChangeDelete: case NSFetchedResultsChangeUpdate: sectionChange[@(type)] = @(sectionIndex); break; } [self.sectionChanges addObject:sectionChange]; } - (void)controller:(NSFetchedResultsController *)controller didChangeObject:(id)anObject atIndexPath:(NSIndexPath *)indexPath forChangeType:(NSFetchedResultsChangeType)type newIndexPath:(NSIndexPath *)newIndexPath { NSMutableDictionary *objectChange = [NSMutableDictionary new]; switch(type) { case NSFetchedResultsChangeInsert: objectChange[@(type)] = newIndexPath; break; case NSFetchedResultsChangeDelete: case NSFetchedResultsChangeUpdate: objectChange[@(type)] = indexPath; break; case NSFetchedResultsChangeMove: objectChange[@(type)] = @[indexPath, newIndexPath]; break; } [self.objectChanges addObject:objectChange]; } - (void)controllerDidChangeContent:(NSFetchedResultsController *)controller { UITableView *tableView = self.tableView; NSUInteger totalChanges = self.sectionChanges.count + self.objectChanges.count; if (totalChanges > 0) { [tableView beginUpdates]; if (self.sectionChanges.count > 0) { for (NSDictionary *change in self.sectionChanges) { [change enumerateKeysAndObjectsUsingBlock:^(NSNumber *key, id obj, BOOL *stop) { NSFetchedResultsChangeType type = [key unsignedIntegerValue]; switch (type) { case NSFetchedResultsChangeInsert: [tableView insertSections:[NSIndexSet indexSetWithIndex:[obj unsignedIntegerValue]] withRowAnimation:UITableViewRowAnimationAutomatic]; break; case NSFetchedResultsChangeDelete: [tableView deleteSections:[NSIndexSet indexSetWithIndex:[obj unsignedIntegerValue]] withRowAnimation:UITableViewRowAnimationAutomatic]; break; case NSFetchedResultsChangeUpdate: [tableView reloadSections:[NSIndexSet indexSetWithIndex:[obj unsignedIntegerValue]] withRowAnimation:UITableViewRowAnimationAutomatic]; break; } }]; } } else if (self.objectChanges > 0) { NSMutableArray *indexPathsForUpdatedObjects = [NSMutableArray new]; for (NSDictionary *change in self.objectChanges) { [change enumerateKeysAndObjectsUsingBlock:^(NSNumber *key, id obj, BOOL *stop) { NSFetchedResultsChangeType type = [key unsignedIntegerValue]; switch (type) { case NSFetchedResultsChangeInsert: [tableView insertRowsAtIndexPaths:@[obj] withRowAnimation:UITableViewRowAnimationAutomatic]; break; case NSFetchedResultsChangeDelete: [tableView deleteRowsAtIndexPaths:@[obj] withRowAnimation:UITableViewRowAnimationAutomatic]; break; case NSFetchedResultsChangeUpdate: [indexPathsForUpdatedObjects addObject:obj]; //[tableView reloadRowsAtIndexPaths:@[obj] withRowAnimation:UITableViewRowAnimationAutomatic]; break; case NSFetchedResultsChangeMove: [tableView moveRowAtIndexPath:obj[0] toIndexPath:obj[1]]; break; } }]; } [tableView endUpdates]; for (NSIndexPath *indexPath in indexPathsForUpdatedObjects) if ([tableView.indexPathsForVisibleRows containsObject:indexPath]) [self updateCell:[tableView cellForRowAtIndexPath:indexPath] atIndexPath:indexPath]; } [self.sectionChanges removeAllObjects]; [self.objectChanges removeAllObjects]; } else if (totalChanges < 1) { [tableView reloadData]; } } - (NSMutableArray *)sectionChanges { if (!_sectionChanges) _sectionChanges = [NSMutableArray new]; return _sectionChanges; } - (NSMutableArray *)objectChanges { if (!_objectChanges) _objectChanges = [NSMutableArray new]; return _objectChanges; }

请注意，此解决方案并不完美，因为如果对部分进行更改并且这些对象位于未更新的部分中，则不会更新对象。应该很容易修复（并且与许多应用程序无关）。

Answer 3

您可以记下数据源中的最后一个索引路径＆amp;然后这样做 -

    NSIndexPath *indexPath     = nil;
    NSMutableArray *newResults = [[NSMutableArray alloc] init];
    if(gLastResultIndex < [self.dataSource count])
    {
        for(int i=(gLastResultIndex); i<[self.dataSource count]; i++)
        {
            indexPath = [NSIndexPath indexPathForRow:i inSection:0];
            [newResults addObject:indexPath];
        }
        [self.table beginUpdates];
        [self.table insertRowsAtIndexPaths:newResults withRowAnimation:UITableViewRowAnimationNone];
        [self.table endUpdates];
    }
    [newResults release];

这有选择地向现有UITableView添加新行。重装表重新加载表中您可能不需要的所有单元格。我只在整个数据源发生变化时使用重载表...

如何从NSFetchedResultsControllerDelegate实现延迟/批量表视图更新？

3 个答案: